Patent Application
20250041940
The present invention relates to a method of preparing spherical metal powder, and more specifically, to a method of preparing spherical metal powder that may prepare titanium or titanium alloy spherical powder in a simple and easy manner using granular powder.
As a conventional method for producing metal powder, a mechanical grinding method using compression grinding or milling, a chemical preparation method such as gas or thermal decomposition and a gas phase or liquid phase precipitation method, or a spraying method in which molten metal is sprayed using a refrigerant such as gas or water is largely known.
The mechanical grinding method not only consumes a large amount of energy, but also has the problem of making it difficult to control the shape of the particles to spheres, and the chemical preparation is advantageous for preparing ultra-fine metal powder, but there are limitations to mass production as it must be prepared under highly controlled conditions using expensive raw materials, and there is also the problem of generating a large amount of toxic wastewater. In addition, although the spraying method is the most commercial method favorable for mass production, the size and shape of particles change very sensitively depending on process parameters such as melt injection rate, refrigerant spraying pressure or nozzle rotation speed, and thus establishing process conditions is very difficult, and it is difficult to completely suppress the surface reaction such as oxidation or nitration caused by the refrigerant, so powder deterioration is likely to occur.
Meanwhile, granular powder is a technology used in pharmaceuticals and agriculture, and when using ceramics or metals, it is a technology used to make granular powder to facilitate molding. In addition to improving physical properties and processes, powder metallurgy using such granular powder has many advantages such as easy mass production, reduced process loss, and sophisticated processing. Powder metallurgy is often used to create products composed of pure metals or metal alloys. Titanium is one exemplary metal used in powder metallurgy. Titanium is a lightweight, high-melting point material with excellent specific strength and corrosion resistance and has been used in the aerospace industry, petrochemical industry, automobile industry, and the like, and recently its application fields are gradually expanding to the medical industry and leisure industry. However, titanium is expensive and it requires a lot of cost to produce titanium parts through cutting and casting, so there are limits to its use in all industries.
The present invention is intended to solve the problems of the related art described above, and the object of the present invention is to provide a method of preparing spherical metal powder that may prepare titanium or titanium alloy spherical powder in a simple and easy manner using granular powder.
In order to achieve the above object, one aspect of the present invention provides a method of preparing spherical metal powder, including: (a) mixing an ultra-fine raw metal with a binder and a solvent to form a slurry; (b) granulating the slurry through spray drying to form granular powder; (c) adding a separating agent to prevent sintering between the granular powder particles; (d) continuously performing degreasing and sintering on the granular powder to form spherical metal powder; (e) performing deoxidation treatment by adding a deoxidizer to achieve high purity of the sintered spherical metal powder; and (f) removing the separating agent and oxide from the deoxidized spherical metal powder.
In one embodiment of the present invention, the spherical metal powder may be selected from the group consisting of CP—Ti-based alloys, Ti—Al-based alloys, Ti—Al—V-based alloys, and a combination thereof.
In one embodiment of the present invention, a particle size range of the spherical metal powder may be 1 to 300 μm.
In one embodiment of the present invention, the ultra-fine raw metal may be one or more selected from the group consisting of titanium hydride, titanium, aluminum, vanadium, tin, palladium, nickel, molybdenum, chromium, cobalt, zirconium, zirconium hydride, niobium, and a combination thereof.
In one embodiment of the present invention, the ultra-fine raw metal may be prepared from a raw material selected from the group consisting of titanium sponge, titanium scrap, and a combination thereof.
In one embodiment of the present invention, in step (a), the solvent may include water and ethyl alcohol, the binder includes a polyvinyl pyrrolidone (PVP) binder, which are physically mixed using a mixing device.
In one embodiment of the present invention, in step (a), 100 to 500 ml of ethyl alcohol, 50 to 650 g of an ultra-fine raw metal, and 16 to 150 ml of PVP may be mixed with respect to 1 L of water.
In one embodiment of the present invention, in step (b), the spray drying may be performed by intermittently spraying the slurry at a pneumatic pressure of 2 to 8 kg/cm2 in a chamber maintained at a vacuum of 10−1 torr or less to form granular powder.
In one embodiment of the present invention, a particle size range of the granular powder may be 1 to 300 μm.
In one embodiment of the present invention, in step (b), the granular powder that is outside the particle size range after granulation may be re-granulated.
In one embodiment of the present invention, in step (c), the separating agent may include MgO powder, K2O powder, or a mixture thereof.
In one embodiment of the present invention, in step (d), a degreasing initial vacuum degree may be 10−6 to 10−2 torr.
In one embodiment of the present invention, in step (d), a degreasing temperature may be 100 to 500° C., and a temperature increase rate may consist of two stages of 2 to 8° C./min and 9 to 20° C./min.
In one embodiment of the present invention, in step (d), a sintering temperature may be 600° C. to 1500° C.
In one embodiment of the present invention, in step (d), a sintering temperature increase rate may consist of two stages of 2 to 8° C./min and 9 to 20° C./min, and a sintering holding time may be 1 min to 50 h.
In one embodiment of the present invention, in step (d), sintering may be performed until pores inside the granular powder are controlled to 10% or less.
In one embodiment of the present invention, in step (d), sintering may be performed until pores inside the granular powder are controlled to 5% or less.
In one embodiment of the present invention, in step (e), the deoxidizer may be Ca gas, Mg gas, or a combination thereof.
In one embodiment of the present invention, in step (e), a deoxidation initial vacuum degree may be 10−6 to 10−2 torr.
In one embodiment of the present invention, in step (e), a deoxidation temperature may be 800 to 1100° C.
In one embodiment of the present invention, a deoxidation temperature increase rate may be 5 to 10° C./min, and a deoxidation holding time after the temperature increase may be 1 to 5 h.
In one embodiment of the present invention, in step (f), the deoxidized spherical metal powder may be pickled and washed with water in dilute hydrochloric acid, dilute sulfuric acid, or a mixture thereof to remove remaining oxides.
In one embodiment of the present invention, in step (f), the spherical metal powder from which the separating agent and oxide have been removed may be dried at 50 to 150° C.
In one embodiment of the present invention, in step (f), a drying time may be 1 min to 5 h.
According to one aspect of the present invention, spherical metal powder with a particle size of 1 to 300 micrometers can be prepared using simple processes of slurry preparation, granulation, degreasing, sintering, deoxidation, washing and drying, and furthermore, not only a single spherical metal powder but also a spherical alloy powder including two or more metals can be easily prepared.
In addition, as a separating agent is first mixed before degreasing and sintering the granular powder, and then degreasing and sintering are continuously performed, the number of heat treatments can be reduced to one, and thus a preparation process can be simplified.
The effect of the present invention is not limited to the above-described effects, and it should be understood to include all effects that can be inferred from the configurations described in the detailed description or claims of the present invention.
Hereinafter, one aspect of the present invention will be described with reference to the accompanying drawings. However, the present invention may be implemented in several different forms, and thus is not limited to the embodiments described herein. In order to clearly illustrate the present invention in the drawings, parts irrelevant to the description are omitted, and the same reference numerals are given to the same or similar parts throughout the specification.
Throughout the specification, when a part is “connected” to another part, this includes not only the case where it is “directly connected” but also the case where it is “indirectly connected” with another member interposed therebetween. In addition, when a part is said to “include” a component, this means that other components may be further included, not excluded, unless specifically stated otherwise.
Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.
Referring to
Conventionally, since the granular powder was degreased and then mixed with the separating agent for sintering, two heat treatments were required in the degreasing and sintering processes, however, the spherical metal powder preparation method of the present invention may reduce the number of heat treatments to one by first mixing the separating agent before degreasing and sintering the granular powder, and performing degreasing and sintering continuously to simplify the preparation process.
The spherical metal powder prepared by the preparation method of the present invention may be a pure metal component or an alloy component of two or more metals. Specifically, when using one type of metal powder as an ultra-fine raw metal, a spherical powder of the pure metal component may be prepared, and when using two or more types of metal powders as a raw metal, a spherical powder of the alloy components may be prepared.
According to one embodiment, the spherical metal powder prepared by the preparation method of the present invention may be spherical metal powder selected from the group consisting of CP—Ti-based alloys, Ti—Al-based alloys, Ti—Al—V-based alloys, and a combination thereof.
According to one embodiment, when using one type of metal powder as an ultra-fine raw metal, the ultra-fine raw metal may include one or more metal powders selected from the group including titanium hydride (TiH2), titanium (Ti), and a combination thereof. The titanium hydride (TiH2) powder may be formed by reacting hydrogen gas with titanium sponge or titanium scrap metal. The titanium hydride sponge or titanium scrap may be crushed into powder by milling or other means. The ultra-fine raw metal may also include alloying elements. When using two or more types of metal powders as an ultra-fine raw metal, the ultrafine raw metal may include two or more metal powders selected from the group including titanium hydride (TiH2), titanium (Ti), aluminum (Al), vanadium (V), tin (Sn), palladium (Pd), nickel (Ni), molybdenum (Mo), chromium (Cr), cobalt (Co), zirconium (Zr), zirconium hydride (ZrH2), niobium (Nb), which can be used to produce titanium-based alloys, and a combination thereof.
According to one embodiment, the raw material of the ultra-fine raw metal may be a raw material selected from the group including recovered titanium sponge, titanium scrap, titanium alloy scrap, and a combination thereof. Such titanium sponge, titanium scrap, and titanium alloy scrap may be generated at industrial sites, and are not limited to specific types of sponge and scrap. Raw materials for these ultrafine raw metals may be screened, cleaned, and processed and then crushed into the ultra-fine raw metal by milling or other means.
Hereinafter, the present invention will be looked at in more detail for each step as follows.
The method of preparing spherical metal powder (S100) includes mixing an ultrafine raw metal with a binder and a solvent to form a slurry (S110).
As the ultra-fine raw metal, a fine powder with an average particle diameter of 0.01 to 50 μm and a particle size distribution of 0.001 to 100 μm may be used.
A slurry material includes a solvent that allows the ultra-fine raw metal to have fluidity so that it can be sprayed and a binder that causes the ultra-fine raw metal to agglomerate.
The solvent and binder are volatile, and the solvent may be ethanol, methanol, water hexane, or acetone, and, polyvinyl pyrrolidone (PVP), polyvinyl butyral (PVB), polyvinyl alcohol (PVA), wax, or polyethylene glycol (PEG), or a mixture thereof may be used as the binder. Preferably, water and ethanol may be used as the solvent, and polyvinyl pyrrolidone (PVP) binder may be used as the binder. PVP is very soluble in a polar solvent such as water or alcohol, and has the property of not separating phases or changing other properties during reaction. In addition, PVP leaves almost no residual organic material in the degreasing and sintering processes and is completely burned, making it advantageous for preparing high-purity spherical metal powder. The slurry may also include other components, such as plasticizers, deflocculating agents, surfactants, or a mixture thereof.
According to one embodiment, in the forming of a slurry (S100), the slurry may be formed by mixing 100 to 500 ml of ethyl alcohol, 50 to 650 g of an ultra-fine raw metal, and 16 to 150 ml of PVP with respect to 1 L of water. That is, by lowering a binder content and mixing the slurry at the above ratio, a degreasing process time may be shortened.
Meanwhile, in the forming of a slurry (S100), slurry materials including the ultra-fine raw metal, the solvent, and the binder may be physically mixed using a mixing device. At this time, a stirrer using a propeller may be used as the mixing device. More specifically, a slurry may be formed by inputting the ultra-fine raw metal to a solvent, dispersing the ultra-fine raw metal with an air spray nozzle, then inputting a binder, and mixing it with a stirrer using a propeller.
The method of preparing spherical metal powder (S100) includes granulating the slurry through spray drying to form granular powder (S120).
The slurry formed in the above-described (S110) may be granulated to form substantially spherical granular powder particles, and each granular powder particle includes aggregates of the ultra-fine raw metal.
According to one embodiment, the granular powder may be obtained by spray drying the slurry. At this time, a spray dryer and an atomizer disk may be used in the granulation process. When slurry is sprayed on the atomizer disk rotating at high speed in a spray dryer chamber, the slurry may be granulated into a spherical shape due to surface tension and the attractive force of the binder. The granulated slurry is scattered outward from the disk due to the centrifugal force of the rotating disk, and at this time, since the spray dryer chamber is heated to 50 to 500° C., the solvent included in the slurry evaporates during the spraying process to form solid granular powder. When the granular powder is prepared in this way, the chamber is opened and the granular powder is taken out.
According to one embodiment, in the forming of granular powder (S120), the spray drying may be performed by intermittently spraying the slurry at a pneumatic pressure of 2 to 8 kg/cm2 in a chamber maintained at a vacuum of 10−1 torr or less to form granular powder. In this way, when the slurry is sprayed by increasing the spray pressure difference in a chamber heated to about 300° C. while the inside is maintained in a vacuum, it becomes possible to obtain fine and high-purity granular powder. An average particle diameter of the granular powder particle formed in this way may be 1 to 350 μm.
Meanwhile, in the forming of granular powder (S120), when the average particle diameter of the granular powder particles after granulation is outside the above range and is too small or large, the loss rate in the granulation process may be minimized by re-dispersing the powder through a solvent and re-granulating it.
The method of preparing spherical metal powder (S100) includes adding a separating agent to prevent sintering between granular powder particles (S130).
When the granular powder is sintered directly, a problem may occur where the granular powder particles are combined with each other and the powder properties are lost, and thus a separating agent may be used on the surface of the granular powder to prevent sintering between the granular powder particles.
The separating agent may be an alkali metal oxide with high oxidizing power and may occupy the space between the granular powder particles so that the granular powder particles remain separated during the sintering process. According to one embodiment, the separating agent may include MgO powder, K2O powder, or a mixture thereof.
Meanwhile, the addition of this separating agent may be performed before the degreasing and sintering process. Conventionally, since the granular powder was degreased and mixed with the separating agent for sintering, two heat treatments were required in the degreasing and sintering processes, however, the method of preparing spherical metal powder of the present invention may reduce the number of heat treatments to one by first mixing the separating agent before degreasing and sintering the granular powder, and performing degreasing and sintering continuously in the same furnace to simplify the preparation process.
The method of preparing spherical metal powder (S100) includes continuously performing degreasing and sintering on the granular powder to form spherical metal powder (S140).
The degreasing process may be performed in a number of ways, including thermal degreasing. At this time, when the thermal degreasing method is used, an initial vacuum degree may be 10−6 to 10−2 torr, a degreasing temperature may be 100 to 500° C., and a temperature increase rate may consist of two stages: 2 to 8° C./min and 9 to 20° C./min.
During the degreasing process, some or all of the binder may be removed. Therefore, degreasing may be performed by maintaining the granular powder at a degreasing temperature for a sufficient amount of time to remove a desired amount of a binder. The degreasing time may also vary depending on the type of binder. Degreasing may also be performed until a predetermined amount of binder is removed. The degreased granular powder may maintain a roughly spherical shape with empty spaces between the degreased granules.
Subsequently, the degreased granular powder may be partially or fully sintered at a sintering temperature such that the particles within each granular powder particle are fused together to form sintered spherical metal powder.
According to one embodiment, a sintering temperature during sintering may be 600° C. to 1500° C., a temperature increase rate may consist of two stages of 2 to 8° C./min and 9 to 20° C./min, and a sintering holding time may be 1 min to 50 h. At this time, degreasing and sintering may be performed by one heat treatment in the same furnace to avoid contact with air, which may cause oxidation or contact with oxygen, and simplify the process.
Sintering may proceed until the degreased granular powder particles are completely sintered while remaining separated from each other by a separating agent. Preferably, this may be performed until the pores inside the degreased granular powder are controlled to 10% or less. More preferably, this may be performed until the pores inside the degreased granular powder are controlled to 5% or less.
Degreasing and sintering may be performed in the same furnace to minimize contact with air, which may cause oxidation or contact with oxygen, and to be performed continuously in one heat treatment.
The method of preparing spherical metal powder (S100) includes performing deoxidation treatment by adding a deoxidizer to achieve high purity of the sintered spherical metal powder (S150).
That is, depending on the oxygen content of the sintered spherical metal powder, a deoxidation process may be performed to reduce the oxygen content to an acceptable level and achieve high purity. The deoxidation process may easily reduce the oxygen content of spherical metal powder to approximately 0.3%.
According to one embodiment, the deoxidizer may be Ca gas, Mg gas, or a combination thereof. Specifically, Ca gas, Mg gas, or both may be mixed with the spherical metal powder in a specific ratio depending on the amount of oxygen to be removed. That is, the amount of deoxidizer to be mixed may be determined depending on the oxygen content of the spherical metal powder. Salts, such as calcium chloride, magnesium chloride, or a combination thereof, which will act as a flux or medium to promote the reaction between the deoxidizer and oxygen, may be additionally mixed.
According to one embodiment, the deoxidation process may be performed by inputting a deoxidizer and sintered spherical metal powder into the reactor chamber under an atmosphere having an initial vacuum degree of 10−6 to 10−2 torr, raising the deoxidation temperature to 800 to 1100° C. at a temperature increase rate of 5 to 10° C./min, and then maintaining it for 1 to 5 h. According to one embodiment, the deoxidized spherical metal powder may be spherical Ti or spherical Ti alloy powder with an oxygen content of 0.3% by weight or less.
The method of preparing spherical metal powder (S100) includes removing the separating agent and oxide from the deoxidized spherical metal powder (S160).
According to one embodiment, the deoxidized spherical metal powder may be pickled and washed with water in dilute hydrochloric acid, dilute sulfuric acid, or a mixture thereof to remove remaining oxides. That is, the mixture produced after the deoxidation process may include oxides such as CaO and MgO and a separating agent such as K2O, and such CaO, MgO, and K2O may be leached with an aqueous solution containing an acid such as dilute hydrochloric acid, dilute sulfuric acid, or a mixture thereof.
Thereafter, the final spherical metal powder may be prepared by washing the spherical metal powder from which the separating agent and oxides have been removed with water and ethanol and drying the same at 50 to 150° C. for 1 min to 5 h. At this time, the final spherical metal powder may have a particle size range of 1 to 300 μm, and exhibit a sphericity of 85% or more and a fluidity of 50 sec/50 mg or less, as measured according to ASTM standards.
Ti powder with a particle size of less than 100 μm was used as an ultra-fine raw metal, and 1 L of water, 300 ml of ethyl alcohol, 350 g of Ti powder, and 50 ml of a PVP binder were mixed, and a slurry was prepared with a stirrer using a propeller.
Granular powder was prepared by spray drying the prepared slurry to form spherical granular powder. The slurry was intermittently sprayed on an atomizer disk at a pneumatic pressure of 4 to 6 kg/cm2 with the spray dryer chamber heated to 300 to 400° C. under a vacuum of 10−1 torr or less to prepare granular powder.
Before degreasing and sintering, granular powder and a separating agent were mixed to prevent sintering between granular powder particles. MgO powder was used as the separating agent.
Afterward, the initial vacuum degree in the furnace was set to 10−2 torr or less, and the furnace was heated in two stages at a temperature increase rate of 5° C./min and 10° C./min to degrease the granular powder in a temperature range of 300 to 400° C. Then, for continuous sintering, the furnace was heated in two stages at a temperature increase rate of 5° C./min and 10° C./min to increase the temperature to 900 to 1200° C. and this temperature was maintained for 30 min to sinter the degreased granular powder.
Sintered spherical Ti metal powder with 3.85% by weight of oxygen was deoxidized using a deoxidizer. Ca gas and Mg gas were used as a deoxidizer.
The sintered spherical Ti metal powder, Ca gas, and Mg gas were input into the reactor chamber, heated to 800 to 900° C. at a temperature increase rate of 10° C./min, and then maintained for 3 h in an atmosphere with an initial vacuum degree of 10−2 torr or less.
The mixture including deoxidized spherical Ti metal powder was removed from the reactor chamber and leached with dilute hydrochloric acid for 2 h. Then, the leached product was washed with water and ethanol and dried at 100° C. for 3 h. The final spherical Ti metal powder has a particle size range of 1 to 300 μm and an oxygen content of 0.067% by weight, and exhibits a sphericity of 85% or more and a fluidity of 50 sec/50 mg or less, as measured according to ASTM standards.
The foregoing description of the present invention is for illustrative purposes, and it will be understood by those skilled in the art that embodiments may be easily modified into other specific forms without changing the spirit and essential properties of the present invention. Therefore, it should be understood that the embodiments described above are illustrative in all respects and not restrictive. For example, each component described as a single type may be implemented in a distributed form, and likewise components described as distributed may be implemented in a combined form.
The scope of the present invention is indicated by the following claims, and all changes or modifications derived from the meaning and scope of the claims and their equivalents should be construed as being included in the scope of the present invention.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10-2021-0188469 | Dec 2021 | KR | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/KR2022/016044 | 10/20/2022 | WO |
